1. Field of the Invention
The present invention relates to an image correction method, an image correction apparatus, and an image correction program.
2. Related Background of the Invention
Nuclear medical images obtained by a nuclear medical inspection such as positron emission tomography (hereinafter, referred to as “PET”) and single photon emission computed tomography (hereinafter, referred to as “SPECT”) are widely used for diagnosing various diseases including cancer.
A nuclear medical image can be obtained by administering a medicine labeled with a radioisotope (hereinafter, referred to as a “radiopharmaceutical”) to a subject and detecting the gamma rays directly or secondarily emitted from the administered medicine using a gamma camera etc. In other words, a nuclear medical image is obtained by imaging the distribution of the administered radiopharmaceutical, so that it is suited for the detection of a lesion having a specific function. For example, 2-[18F] fluoro-2-deoxy-D-glucose, which is one of radiopharmaceuticals, has a property of being accumulated on a tumor at which sugar metabolism is raised, so that it becomes possible to specifically detect a tumor at which sugar metabolism is raised.
As described above, the nuclear medical inspection has an advantage of being capable of obtaining nuclear medical images applicable to diagnosis of various diseases by using various radiopharmaceuticals, however, there is a problem in that the image quality of a nuclear medical image is lower than that of a biological tomographic image that can be obtained by other methods such as CT imaging. For example, there is a problem of deterioration in image quality caused by the absorption of gamma rays depending on the distance from a radiation source or a problem of the lowness of contrast at a lesion.
To cope with the former problem, that is, the deterioration in image quality caused by the absorption of gamma rays, there has been proposed a method for correcting a nuclear medical image using an absorption correction map generated from a CT image and taking into account the linear absorption coefficient and the depth from the body surface (Ordered Subset Expectation Maximization method (hereinafter, referred to as an “OSEM”) (for example, refer to Non-patent Document 1 and Non-patent Document 2).
[Non-patent Document 1] Patton, J. A., Delbeke, D. and Sandler, M. P., “Image Fusion Using an Integrated, Dual-Head Coincidence Camera with X-Ray Tube-Based Attenuation Maps.”, The Journal of Nuclear Medicine, (USA), Society of Nuclear Medicine, 2000, 41, 8, p. 1364–1368.
[Non-Patent Document 2] Hudson, H. M. and Larkin, R. S., “Accelerated Image Reconstruction Using Ordered Subsets of Projection Data”, IEEE Transactions on Medical Imaging, (USA), IEEE Engineering in Medicine and Biology Society et al., 1994, 13, 4, p. 601–609.